1. Field of the Invention
The present invention relates to a combined engine which is capable of utilizing either gas fuel or liquid fuel by means of selecting the appropriate operational mode, and which is applied mainly towards generating electricity. This application is based on an patent application No. Hei 10-130849 filed in Japan, the content of which is incorporated herein by reference.
2. Relevant Art
In recent years, gas engines have continued to enjoy wide usage as the key hard of co-generation system. In particular, in commercial district, due to the regulation of exhaust gas, spark-ignition gas engines with a precombustion chamber are being widely employed. On the other hand, diesel engines are also in great demand for use in fire prevention and power maintenance during times of emergency.
Conventionally, the gas and diesel engines for satisfying the aforementioned demands had to be designed separately, as different engine types, since an engine capable of providing both spark ignition and compression ignition in the same engine did not exist. Consequently, a great demand exists for the preparation of a gas engine for use during normal operation, and a diesel engine for use in emergency operation, with large amounts of capital being invested accordingly.
On the other hand, a combined engine exists that is capable of operating in both a gas operational mode in which gas fuel is used, and a diesel operational mode in which liquid fuel is used. According to this type of combined engine, it is possible to selectively switch between a gas operational mode, in which gas fuel is combusted using a small amount of pilot oil (approximately 5.about.15% of the entire fuel amount) as the ignition source, and a diesel operational mode, in which only liquid fuel is combusted. With regard to this engine, at the time of starting the engine, the engine is started and warmed-up by means of liquid fuel which possesses a superior ignitability. After the engine is warmed-up, at the stage where the engine operational load factor reaches at least 30%, by switching from liquid fuel to gas fuel, the highly ignitable liquid fuel that is used as the pilot fuel is supplemented by ignition of the less ignitable gas fuel.
However, according to the conventional combined engines, due to the use of liquid fuel as the pilot fuel, in an amount of approximately 5.about.15% of the entire heating amount, there exists a limit with regard to the NOx, as well as the fall in soot and dust.
In consideration of the aforementioned, it is an object of the present invention is to provide a combined engine and method for operating the same which is capable of utilizing either gas fuel or liquid fuel, while also reducing the equipment costs and decreasing the amount of pollution therefrom.